1. Field of the Invention
The present invention relates to a light measuring device used in a camera or the like, and a computer-readable storage medium used in this device.
2. Related Background Art
FIG. 1 is a view showing a conventional light measuring device.
Referring to FIG. 1, the cathode side of a sensor cell (to be simply referred to as a sensor hereinafter) 1 formed from a photodiode is biased by a predetermined voltage VREF1. The anode side is connected to the inverting terminal of an operational amplifier 2. This operational amplifier 2 and a logarithmic compression diode 3 formed from a transistor diode-connected to the operational amplifier 2 through diode conjunction construct a logarithmic compression circuit 101. The sensor portion of this light measuring device is divided into six sensors S0 to S5, as shown in FIG. 2.
The outputs from these sensors are input to a decoder 12 and switched by control signals AEINT, CSAE0 to CSAE3, and RES. One of the outputs is input to an operational amplifier 13. This operational amplifier 13, a diode 14, a switch 15, and a current source 16 form a dark current compensation circuit 102. The output from this dark current compensation circuit 102 is input to an amplifier 103 constructed by an operational amplifier 17 and resistors 18 to 21 to invert and amplify the signal.
Let Ip be the photocurrent flowing to the sensor 1, and Is be the reverse-direction saturation current of the logarithmic compression diode 3. An output V of the sensor 1 is given by
V=kT/q{ln(Ip/Is)}xe2x80x83xe2x80x83(1)
where k is the Boltzmann""s constant, q is electric charge of the electron, and T is the absolute temperature.
The output V is selected by the decoder 12, output from the dark current compensation circuit 102, and inverted and amplified by the amplifier 103, so a light measurement output AEAD is obtained. Let R1 to R4 be the resistance values of the resistors 18 to 21,
AEAD=xe2x88x92(R2/R1)*(Vxe2x88x92VREF1)+(R2/R3)*VREF1xe2x80x83xe2x80x83(2)
FIG. 3 shows the waveform of pre-emission and the timing of A/D conversion of the light measurement output in a light modulation method of pre-emitting strobo light (flashlight) before photographing by the camera and determining the light emission amount of actual light emission on the basis of the light measurement value at that time.
The light emission time of pre-emission is preferably short because actual light emission must be subsequently performed. Because, when a large energy is consumed in pre-emission, the light emission amount of the actual light emission becomes small. It is difficult to emit strobo light (flashlight) in a predetermined amount for a long time. For this reason, the pre-emission time is suppressed to about 800 xcexcsec.
The light measurement output is A/D-converted and then input to the CPU. To increase the accuracy, the number of times of light measurement must be increased. Conventionally, the sensors S0 to S5 sequentially perform light measurement, and the light measurement outputs are A/D-converted. The time of A/D conversion of one cycle is 10 xcexcsec. A/D conversion is performed eight times for each sensor, i.e., in 80 xcexcsec. For this reason, a high-performance CPU or A/D converter is used.
However, in a system for pre-emitting flashlight before photographing and calculating the light emission amount of actual light emission on the basis of the light measurement value of pre-emission and a light measurement value immediately before pre-emission, the light emission time of pre-emission is limited because actual emission follows pre-emission. When the performance of the conventional A/D converter is taken into consideration, the A/D conversion time per sensor is as long as 10 xcexcsec, as described above. To reduce errors due to, e.g., flicker of a fluorescent lamp, A/D conversion must be performed about eight times for one sensor, and the A/D conversion time becomes as long as 80 xcexcsec.
The sensor switching time or the time after generation of a light emission instruction from the camera until actual light emission need also be taken into consideration. The number of divisions of the sensor may be increased, though the number of sensors is limited to six in the above scheme, as described above.
It is an object of the present invention to obtain an accurate light measurement value in a predetermined light measurement time even when the number of divisions of a sensor is large.
It is another object of the present invention to obtain an accurate light measurement value in a predetermined light measurement time and cope with low luminance to high luminance when the number of divisions of a sensor is large.
In order to achieve the above object, according to an aspect of the present invention, there is provided a light measuring device comprising sensor means for converting input light into an electrical signal, integrating means for integrating the electrical signal output from the sensor means, and control means for selectively setting one of a first mode in which the electrical signal is directly output and a second mode in which a signal obtained by integrating the electrical signal with the integrating means is output.
According, to another aspect of the present invention, there is provided a light measuring device comprising a plurality of sensor means for converting input light into electrical signals, a plurality of integrating means for compressing electrical signals from the plurality of sensors means in parallel to a predetermined level and integrating the compressed electrical signals, and control means for selectively settings one of a first mode, in which the electrical signals from the plurality of sensor means are output without being passed through the plurality of integrating means, and a second mode, in which the electrical signals from the plurality of sensor means are output through the plurality of integrating means.
According to still another aspect, there is provided a computer-readable storage medium which stores a program for executing conversion processing of converting input light into an electrical signal with sensor means, integrating processing of integrating the electrical signal output from the sensor means, first mode processing of directly outputting the electrical signal, second mode processing of outputting a signal obtained by integrating the electrical signal by integrating processing, and control processing of selectively setting one of the first and second modes.